Indirectly heated disk-like cathode

ABSTRACT

An indirectly heated cathode comprising a support for a layer of emissive material secured to a metal container for a heating element. A space formed between the heating element and the support is filled with a sintered metal powder.

United States Patent Kuiper [151 3,681,642 51 Aug. 1,1972

[54] INDIRECTLY HEATED DISK-LIKE CATHODE [72] Inventor: Adrianus Kuiper, Emmaningel,

Eindhoven, Netherlands [73] Assignee: U. S. Phillips Corporation, New

York, N.Y.

[22] Filed: May 21, 1970 [21] App1.No.: 48,594

Related US. Application Data [62] Division of Ser. No. 695,410, Jan. 3, 1968, Pat.

[52] US. Cl. ..3l3/337, 29/2517, 313/270 [51] Int. Cl. ..H0lj 1/20 [58] Field of Search ..313/270, 337; 29/2517 [56] References Cited UNITED STATES PATENTS 2,869,017 1/1959 Levi ..3l3/337X 2,912,611 11/1959 Beck et al. .;....3l3/337 X 3,117,249 1/1964 Winters ..3l3/337 3,221,203 11/1965 Ragland..' ..3l3/337 UX 3,227,911 1/1966 Heil ..313/337 3,175,118 3/1965 Ney ..3l3/337 X 3,265,495 8/1966 Freytag et al. .'..313/337 UX 3,341,917 9/1967 Oyabu et al. ..3l3/337 UX Primary Examiner-David Schonberg Assistant Examiner-Toby H. Kusmer Attorney-Frank R. Trifari 57 ABSTRACT An indirectly heated cathode comprising a support for a layer of emissive material secured to a metal container for a heating element. A space formed between the heating element and the support is filled with a sintered metal powder.

1 Claim, 4 Drawing Figures INDIRECTLY HEATED DISK-LIKE CATHODE This is a division of application Ser. No. 695,410, now U.S. Pat. No. 3,574,910.

The invention relates to an indirectly heated disklike cathode comprising a support for the emitting material which is secured to a metal holder containing the heating element, the space between the heating element and the support being filled with a sintered metal powder.

It is known that the heat transfer between the heating element and the support for the emitting layer of a cathode can be improved when the space between the heating element and the support is entirely filled with sintered metal powder, for exarnple,.nickel powder. A drawback of the known constructions is, however, that asa result of the difference in coefficients of expansion of the various components the sintered metal powder easily works loose from the surface of the support and/or from the surface of the heating'element. A heating element is to be understood to mean in this connection a filament which is coated with insulating material, generally aluminum oxide. Another drawback is that the heat content of the cathode is considerably increased by the comparatively large quantity of metal powder, which causes a prolongation of the heating up time.

The working loose of the metal powder causes ungovernable changes in the distribution of the cathode temperature and/or local overheating of the heating element. It is known to avoid this by making the sintered metal layer porous and somewhat flexible by using a mixture of coarse granular powder of, for example, nickel and a small quantity of fine grains of a different metal, for example, molybdenum or palladium. By heating above the alloying temperature of the metals the fine granular metal connects the coarse grains locally so that a porous mass isv obtained. Although as a result of this the working loose of the metal powder can be avoided, the drawback remains of the increase of the heat mass while the method is complicated.

The said drawbacks can be avoided substantially en- FIG'. 1 is a perspective view of support and a holder prior to welding, and

FIG. 2is a cross-sectional view during welding of the holder to the support:

FIG. 3 shows the holder andthe heating element prior to assembling, and;

FIG. 4-is across-sectional viewrof a cathode accord- I ing'to the-invention.

tirely by using the method according to the invention,

inwhich the holder for the heating element is formed like a cap the end face of which comprises anaperture, which holder is welded against the support with its end face in such a manner that as a result of the pressure and the local heating during welding, agap having a wedgelike cross-section is formed between the inwardly directed edge of the end face and the support, after which the heating element which is dipped in a suspension of a suitable metal powder, is provided in the holder and the metal powder is released, for. exam.- ple, by dipping the support with the holder in a solvent for the suspension medium of the metal powder, so that it flows into the space between the support and the heating element and into the gap and fills it after which the solvent and the suspension medium are removed. by heating and the metal powder is sintered after which the support is provided with emitting material. The lower side of the holder is preferably closed by means of a cover. This cover preferably consists of metal and may be formed integral with the holder; Alternatively a few connection strips may be present and be formed integral with the holder.

The invention will now be described with reference to the accompanying drawing, in which,

Referring now'to the Figures, reference numeral 1 denotesathe support for the emitting material, 2 denotes the holder for the heating element 8. The end face 3 of theholder 2 comprises an aperture 4. A cover 5 is formed integral withtheholder-Z as well as the connectionstrips 14; Theholder 2 is forced against the support 1 with the edge. of its end face (FIG. 2) by means of a hollowweldingterminal 6 and a flat welding terminal 7. The welding. terminal 6 terminates in a sharp edge-so that theholder 2 after. welding is connected to the-support 1 by means of a ring weld 13 (FIG. 3), insteadof a ring weld, a number of separate welds may alternatively beused. Asa result of the pressure and the high local heating of the edge 3 during welding, the edge 3 bends inwardly so that a gap 12 which in this case is annular and'has a wedge-like cross-section is formed within the edge3-and the support 1. The heating element 8. consisting of a tungsten filament 10 which; is embedded in aluminum oxide, is dipped in a suspension consisting of nickel powder and a binder, for example, nitrocellulose, so that a layer 9 of this suspension covers the heating element 8. The heating element8, after drying of the layer 9, is forced into the holder 2, the cover 5 is closed. and the assembly is dipped in a solvent of the said binder, for example,

acetone. The binder dissolves and the metal powder flows into the cavity between the element 8, the support 1 andthe holder 2 fills the wedge-like gap 12. The metal powder is then sintered, during which the binder burns away. The sintered metal particles provide a ready heat conduction between the element 8 and the support 1 without the heat. content of the cathode being increased noteworthily. As aresult of the. small quantity and the thin layer of metal powder, the expansion also is negligible so that working loose of the layer of metal powder from the support does not occur, the more so since the thin-walled edge 3 is flexible so that mechanical stresses in the material remain small.

The support 1' is then provided with a layer 11 of barium-strontium carbonate and the connection strips 14 are bent to the correct shape after which the cathode, a cross-section of which is shown in FIG. 4, can be incorporated in an electron gun or a discharge tube.

In a particular embodiment the diameter of the cathode was 1.2 mm, the thickness 0.33 mm. The holder 2' was of a nickel-iron alloy, the coefficient of expansion of which is approximately X 1 0 and which corresponds to that of the tungsten of the filament 20. The thickness of the support was 50 microns, the wall thickness of'the holder 2 was 20 a. The grain size of the nickel powder 9 was from 1 to 10 t.

Instead of a nickel support 1 coated with emitting material, a porous support 1 compressed from tungsten powder may alternatively be used and afterwards be impregnated with emitting material. A profiled support 1 may alternatively be used which may comprise an emitting pill. Instead of nickel powder 9, a powder of any of the commonly used known metals, for example, tungsten, palladium; or molybdenum may be used.

What is claimed is: 1. An indirectly heated, disk-like cathode comprising a support having a layer of emissive material thereon,a cup-shaped member housing a heating element and- 

